The present invention relates to a laminated motor core, a method of manufacturing such a laminated core, a motor incorporated with such a laminated core, and an ink-jet recording apparatus provided with such a motor, and particularly relates to restraint of vibrations of a laminated core used in a stepping motor, a servo motor, or the like.
Conventionally, a laminated core to be used as a stator core of a stepping motor or the like is formed in such a structure that a plurality of core pieces 10 of magnetic material are laminated, similarly to that which is shown in FIGS. 1 and 2. Each core piece 10 is formed with such a flat shape as illustrated, by progressive forming by a press, in advance. Thereafter, one core piece 10 is put on the top of another core piece 10, and half blanking is performed in caulking portions 14 as illustrated so that the two core pieces 10 are fitted and fixed to each other. Such a process is repeated to fix a large number of core pieces 10 to each other sequentially to thereby form a laminated core 1.
The laminated core 1 is provided with an outer frame portion 11 formed in the outer circumferential portion, and teeth portions 18 formed in the inner circumferential portion. The teeth portions 18 are constituted by, for example, eight bridge portions 12 projecting inward from the inner circumferential surface of the outer frame portion 11, and magnetic pole portions 13 formed on the forward ends of these bridge portions 12, respectively. A surface-roughed shape constituted by mountain portions 13a and groove portions 13b formed alternately in the direction of rotation of a not-shown rotor is formed in the inner circumferential edge portion of each of the magnetic pole portions 13. The area surrounded by these eight magnetic pole portions 13 forms an inner hole 16 which is substantially circular, so that a not-shown rotor is received in this inner hole 16.
However, in a motor in which such a laminated core as mentioned above is used as a stator core, large noise may be caused when the motor is driven. Though this noise is considered to be caused for various reasons, the present inventors have found, through various analyses, that the main reason is in that the core pieces 10 of the stator core vibrate in the vicinities of the magnetic pole portions 13, and the core pieces 10 resonate in the case where a certain condition is satisfied.
In order to restrain such vibrations or resonance, it is considered necessary to fix the core pieces 10 to each other at a portion each of the teeth portions 18.
Therefore, caulking portions 15 was provided in the bridge portions 12 of the respective teeth portions by way of experiment. As a result, it was found that the above-mentioned vibrations or resonance could be reduced effectively. However, in this case, the number of the caulking portions 15 increased correspondingly to the number of the teeth portions 18, so that not only it was necessary to make mold adjustment which requires high technique and skill, but also the durability of the mold was required unreasonably. Accordingly, the manufacturing cost was increased.
Further, caulking portions were provided in the magnetic pole portions 13 of the teeth portions 18 by way of experiment. In this case, not only it was difficult to perform half blanking but also it was difficult to ensure the strength of the mold because the plane shapes of the respective core pieces 10 are formed to be narrow in the magnetic pole portions 13. Accordingly, manufacturing was difficult in practical use.
Furthermore, another method in which the core pieces 10 are bonded with each other by a bonding agent or tape with a bonding agent may be considered. However, not only it is comparatively difficult to automate this bonding process and it requires high cost to provide equipment therefor, but also there is such a danger that the bonding agent is eluted in the process of cleansing the stator core to make the core pieces 10 separate from each other.
It is an object of the present invention to provide a laminated motor core in which vibrations of core pieces causing motor noise can be restrained at a low cost, and a method of manufacturing such a laminated core.
It is another object of the present invention to provide a motor and an ink-jet recording apparatus, in which noise is prevented from being made.
(1) According to an aspect of the present invention, provided is a laminated core of a motor in which a plurality of magnetic plates are laminated one on another, the laminated core being provided with magnetic poles each having a roughed surface constituted by mountain portions and groove portions formed alternately in the direction of rotation of the motor, characterized in that welded portions for firmly fixing the magnetic plates to each other are provided in surfaces of the groove portions formed in the magnetic poles. According to this invention, the welded portions for firmly fixing the magnetic plates to each other are provided in the surfaces of the groove portions of the magnetic poles, so that it is possible to firmly fix the magnetic plates to each other in the magnetic poles to which a magnetic force is applied. Accordingly, it is possible to restrain the generation of vibrations, so that it is possible to reduce motor noise. In addition, the welded portions are formed in the groove portions where the magnetic flux density is small, so that it is possible to restrain deterioration of the magnetic characteristic caused by heat at the time of welding.
(2) According to another aspect of the present invention, in the laminated core of a motor described above in the item (1), the welded portion is provided in the surface of the groove portion formed in the vicinities of the central portion of each of the magnetic poles in the direction of rotation. As is understood from magnetic flux density distribution and magnetic flux distribution in FIGS. 4 and 5 which will be described later, the magnetic flux density becomes lowest, for example, to be in a range of from 2,500 to 5,000 gausses in the groove portions near the central portions of the magnetic poles. Since the welded portions are formed in such positions (near the central portions of the magnetic pole portions in the direction of rotation), it is possible to further reduce the deterioration of the magnetic characteristic, and it is also possible to obtain symmetry of a fixation force in the magnetic pole portions to thereby make it possible to restrain the generation of vibrations efficiently.
(3) According to a further aspect of the present invention, in the laminated core of a motor described in the above item (1), the welded portions are provided in the surfaces of the groove portions respectively formed on opposite end sides of each of the magnetic poles in the direction of rotation. On the opposite end dies of each magnetic pole, vibrations with large amplitude are apt to be produced because the opposite end sides are in the most distant positions from the base of the bridge portion. Since the welded portions are provided in such portions, it is possible to restrain vibrations effectively.
(4) According to another aspect of the present invention, provided is a laminated core of a motor in which a plurality of magnetic plates are laminated one on another, the laminated core being provided with magnetic poles each having a roughed surface constituted by mountain portions and groove portions formed alternately in the direction of rotation of the motor, characterized in that welded portions for firmly fixing the magnetic plates to each other are provided on both back-surface-side shoulder portions of each of the magnetic poles. The magnetic flux density is a comparatively small in the back-surface-side shoulder portions of the magnetic poles. Accordingly, deterioration of the magnetic characteristics caused by heat at the time of welding is too small to give a bad influence to the characteristics of the motor.
(5) According to a further aspect of the present invention, provided is a laminated core of a motor in which a plurality of magnetic plates are laminated one on another, the laminated core being provided with magnetic poles each having a roughed surface constituted by mountain portions and groove portions formed alternately in the direction of rotation of the motor, characterized in that welded portions for firmly fixing the magnetic plates to each other are provided on both side surfaces of each of bridge portions connecting the magnetic poles with an outer frame. Though the magnetic flux density is comparative large in the both sides of each of the bridge portions, the bridge portion is comparatively wide (in comparison with the mountain portions of the magnetic poles). Therefore, it gives no bad influence to the characteristic of the motor even if there is some deterioration of the magnetic characteristic caused by heat at the time of welding.
(6) According to a still further aspect of the present invention, in the laminated core of a motor described in any one of the above items (1) to (5), each of the welded portions is extended in the direction of lamination of the magnetic plates and formed integrally. Since the welded portions are formed integrally so as to extend in the direction of lamination of the magnetic plates, it is not necessary to position and weld the welded portions in bonded portions of the thin magnetic plates so that it is possible to form the welded portions rapidly and inexpensively.
(7) According to another aspect of the present invention, in the laminated core of a motor described in the above item (6), each of the welded portions is formed so that a plurality of welded spots are disposed to overlap each other in the direction of lamination. Since the welding process can be performed discontinuously in the direction of lamination, light radiation can be performed discontinuously, so that it is possible to reduce the output and load of the apparatus while it is possible to give high welding energy to the welded portions. In addition, since the welded spots are overlapped each other, it is possible to prevent a failure in the welding process caused by discontinuous formation of the welded portions.
(8) According to a further aspect of the present invention, in the laminated core of a motor described in any one of the above items (1) to (7), the welded portions are formed by welding by laser radiation. Places to be welded can be welded at a high accuracy and at a high speed by laser radiation even if the places are comparatively small areas and exist in deep portions such as grooves of a stator core.
(9) According to a still further aspect of the present invention, provided is a method of manufacturing a laminated core of a motor in which a plurality of magnetic plates are laminated one on another, the laminated core being provided with magnetic poles each having a roughed surface constituted by mountain portions and groove portions formed alternately in the direction of rotation of the motor, characterized in that a welding process for firmly fixing the magnetic plates to each other is given to surfaces of the groove portions formed in the magnetic poles. As the conditions used here for the welding process, the respective magnetic plates have to be welded sufficiently, and deterioration of the magnetic characteristic caused by heat at the time of welding should be avoided. However, as a result of experiments, it was found that a satisfactory result could be obtained easily even if no special conditions were taken so long as conditions within a scope which were ordinarily selected by those skilled in the art as welding conditions were taken. This welding process is, for example, applied onto the surfaces of the groove portions formed in the vicinities of central portions or in the opposite end of the respective magnetic poles in the direction of rotation. Furthermore, the welding process may be applied onto places other than the groove portions of the magnetic poles, for example, two back-surface-side shoulder portions of each of the magnetic poles, or both side surfaces of the bridge portion connecting each magnetic pole with the outer frame portion.
(10) According to another aspect of the present invention, in the method of manufacturing a laminated core described in the above item (9), the welding process is continuously given in the direction of lamination of the magnetic plates. By giving the welding process continuously in the direction of lamination, it is possible to perform the welding process rapidly and without much labor.
(11) According to a further aspect of the present invention, in the method of manufacturing a laminated core of a motor described in the above item (9) or (10), the welding process is performed by scanning with light spots in the direction of lamination of the magnetic plates so that the magnetic substances per se are melted by the heat of the light spots to thereby perform the welding process. Of course the welding process can be performed by using bonding material attached to the surfaces of the groove portions. But, even by welding the surfaces per se of the groove portions, it is possible to obtain a sufficient fixation force while avoiding the influence on the magnetic characteristic.
(12) According to a still further aspect of the present invention, in the method of manufacturing a laminated core of a motor described in the above item (11), scanning with the light spots is performed discontinuously at such an interval that spot areas are overlapped each other in the direction of lamination. Since the welding process can be performed discontinuously in the direction of lamination, it is possible to perform light radiation discontinuously. Accordingly, it is possible to reduce the output and load of the apparatus while it is made possible to give high welding energy to the welded portions. In addition, since the welded spots are overlapped each other, it is possible to prevent a failure of the welding process caused by discontinuous formation of the welded portions.
(13) According to another aspect of the present invention, in the method of manufacturing a laminated core of a motor described in the above item (11) or (12), the light spots and the laminated core are moved relatively in the direction of the laminated core while keeping a predetermined angle. By relatively moving the light spots and the laminated core in the direction of lamination while keeping the incident angle of light flux, it is possible to keep the light spots in a predetermined shape at the time of scanning. Accordingly, it is possible to perform heating stably with a stable energy density within a stable irradiation region, so that it is possible to reduce a welding failure of the magnetic plates and it is possible to perform heating at a minimum because of the enhancement of stability. Accordingly, it is possible to restrain deterioration of the magnetic characteristic of the magnetic poles due to heating.
(14) According to a further aspect of the present invention, in the method of manufacturing a laminated core of a motor described in any one of the above items (9) to (13), the welding process is performed by laser radiation. Places to be welded can be welded at a high accuracy and at a high speed by laser radiation even if the places are comparatively small areas and exist in deep portions such as grooves of a stator core. This method is particularly suitable for welding such a laminated core. It has been found that this welding by laser radiation is preferably performed under conditions that the radiation power of laser light is limited to some extent.
(15) According to a still further aspect of the present invention, provided is a motor in which a laminated core of a motor described in any one of the above items (1) to (8) is incorporated as a stator core. It is therefore possible to obtain a motor in which noise is restrained.
(16) According to another aspect of the present invention, provided is an inkjet recording apparatus in which a motor described in the above item (15) is mounted as a driving source of a paper feeding mechanism or an ink-jet head feeding mechanism. It is therefore possible to obtain an inkjet recording apparatus in which noise is in a low level during printing.